﻿using System;
using System.Collections.Generic;
using System.Text;
using TimersXP.Helpers;
using System.Diagnostics.CodeAnalysis;

namespace TimersXP.Messaging
{
    /// <summary>The Messenger is a class allowing objects to exchange messages.</summary>
    public class Messenger : IMessenger
    {
        private static Messenger defaultInstance;

        private Dictionary<Type, List<WeakActionAndToken>> recipientsOfSubClassesAction;

        private Dictionary<Type, List<WeakActionAndToken>> recipientsStrictAction;

        /// <summary>Gets the Messenger's default instance, allowing to register and send messages in a static manner.</summary>
        /// <value>The default messenger instance.</value>
        public static Messenger Default
        {
            get
            {
                if (defaultInstance == null)
                    defaultInstance = new Messenger();
                return defaultInstance;
            }
        }

        /// <summary>Provides a way to override the Messenger.Default instance with a custom instance, for example for unit testing purposes.</summary>
        /// <param name="newMessenger">The instance that will be used as Messenger.Default.</param>
        public static void OverrideDefault(Messenger newMessenger) { defaultInstance = newMessenger; }

        /// <summary>Sets the Messenger's default (static) instance to null.</summary>
        public static void Reset() { defaultInstance = null; }

        /// <summary>
        /// Registers a recipient for a type of message TMessage. The action parameter will be executed when a corresponding message is sent.
        /// <para>Registering a recipient does not create a hard reference to it, so if this recipient is deleted, no memory leak is caused.</para>
        /// </summary>
        /// <typeparam name="TMessage">The type of the message that the recipient registers for.</typeparam>
        /// <param name="recipient">The recipient that will receive the messages.</param>
        /// <param name="action">The action that will be executed when a message of type TMessage is sent.</param>
        public virtual void Register<TMessage>(object recipient, Action<TMessage> action) { Register(recipient, null, false, action); }

        /// <summary>
        /// Registers a recipient for a type of message TMessage. The action parameter will be executed when a corresponding message is sent.
        /// See the receiveDerivedMessagesToo parameter for details on how messages deriving from TMessage (or, if TMessage is an interface,
        /// messages implementing TMessage) can be received too.
        /// <para>Registering a recipient does not create a hard reference to it, so if this recipient is deleted, no memory leak is caused.</para>
        /// </summary>
        /// <typeparam name="TMessage">The type of message that the recipient registers for.</typeparam>
        /// <param name="recipient">The recipient that will receive the messages.</param>
        /// <param name="receiveDerivedMessagesToo">If set to <c>true</c>, message types deriving from TMessage will also be transmitted to the recipient.
        /// For example, if a SendOrderMessage and an ExecuteOrderMessage derive from OrderMessage, registering for OrderMessage and setting receiveDerivedMessagesToo
        /// to true will send SendOrderMessage and ExecuteOrderMessage to the recipient that registered.
        /// <para>Also, if TMessage is an interface, message types implementing TMessage will also be transmitted to the recipient. For example, if a SendOrderMessage
        /// and an ExecuteOrderMessage implement IOrderMessage, registering for IOrderMessage and setting receiveDerivedMessagesToo to true will send SendOrderMessage 
        /// and ExecuteOrderMessage to the recipient that registered.</para></param>
        /// <param name="action">The action that will be executed when a message of type TMessage is sent.</param>
        public virtual void Register<TMessage>(object recipient, bool receiveDerivedMessagesToo, Action<TMessage> action) { Register(recipient, null, receiveDerivedMessagesToo, action); }

        /// <summary>
        /// Registers a recipient for a type of message TMessage. The action parameter will be executed when a corresponding message is sent.
        /// <para>Registering a recipient does not create a hard reference to it, so if this recipient is deleted, no memory leak is caused.</para>
        /// </summary>
        /// <typeparam name="TMessage">The type of the message that the recipient registers for.</typeparam>
        /// <param name="recipient">The recipient that will receive the messages.</param>
        /// <param name="token">A token for a messaging channel, If a recipient registers using a token, and a sender sends a message using the same token,
        /// then this message will be delivered to the recipient. Other recipients who did not use a token when registering (or who used a different token)
        /// will not get the message. Similarly, messages sent without any token, or with a different token, will not be delivered to that recipient.</param>
        /// <param name="action">The action that will be executed when a message of type TMessage is sent.</param>
        public virtual void Register<TMessage>(object recipient, object token, Action<TMessage> action) { Register(recipient, token, false, action); }

        /// <summary>
        /// Registers a recipient for a type of message TMessage. The action parameter will be executed when a corresponding message is sent.
        /// See the receiveDerivedMessagesToo parameter for details on how messages deriving from TMessage (or, if TMessage is an interface,
        /// messages implementing TMessage) can be received too.
        /// <para>Registering a recipient does not create a hard reference to it, so if this recipient is deleted, no memory leak is caused.</para>
        /// </summary>
        /// <typeparam name="TMessage">The type of message that the recipient registers for..</typeparam>
        /// <param name="recipient">The recipient that will receive the messages.</param>
        /// <param name="token">A token for a messaging channel. If a recipient registers using a token, and a sender sends a message using the same token,
        /// then this message will be delivered to the recipient. Other recipients who did not use a token when registering (or who used a different token)
        /// will not get the message. Similarly, messages sent without any token, or with a different token, will not be delivered to that recipient.</param>
        /// <param name="receiveDerivedMessagesToo">If set to <c>true</c>, message types deriving from TMessage will also be transmitted to the recipient. For example,
        /// if a SendOrderMessage and an ExecuteOrderMessage derive from OrderMessage, registering for OrderMessage and setting receiveDerivedMessagesToo to true will
        /// send SendOrderMessage and ExecuteOrderMessage to the recipient that registered.
        /// <para>Also, if TMessage is an interface, message types implementing TMessage will also be transmitted to the recipient. For example, if a SendOrderMessage
        /// and an ExecuteOrderMessage implement IOrderMessage, registering for IOrderMessage and setting receiveDerivedMessagesToo to true will send SendOrderMessage
        /// and ExecuteOrderMessage to the recipient that registered.</para>.</param>
        /// <param name="action">The action that will be executed when a message of type TMessage is sent.</param>
        public virtual void Register<TMessage>(object recipient, object token, bool receiveDerivedMessagesToo, Action<TMessage> action)
        {
            var messageType = typeof(TMessage);

            Dictionary<Type, List<WeakActionAndToken>> recipients;

            if (receiveDerivedMessagesToo)
            {
                if (recipientsOfSubClassesAction == null)
                    recipientsOfSubClassesAction = new Dictionary<Type, List<WeakActionAndToken>>();

                recipients = recipientsOfSubClassesAction;
            }
            else
            {
                if (recipientsStrictAction == null)
                    recipientsStrictAction = new Dictionary<Type, List<WeakActionAndToken>>();

                recipients = recipientsStrictAction;
            }

            List<WeakActionAndToken> list;

            if (!recipients.ContainsKey(messageType))
            {
                list = new List<WeakActionAndToken>();
                recipients.Add(messageType, list);
            }
            else
                list = recipients[messageType];

            var weakAction = new WeakAction<TMessage>(recipient, action);
            var item = new WeakActionAndToken
            {
                Action = weakAction,
                Token = token
            };
            list.Add(item);

            Cleanup();
        }

        /// <summary>Sends a message to the registered recipients. The message will reach all recipients that registered for this message type using one of the Register methods.</summary>
        /// <typeparam name="TMessage">The type of the message that will be sent.</typeparam>
        /// <param name="message">The message to send to registered recipients.</param>
        public virtual void Send<TMessage>(TMessage message) { SendToTargetOrType(message, null, null); }

        /// <summary>
        /// Sends a message to registered recipients. The message will reach only recipients that registered for this message type
        /// using one of the Register methods, and that are of the targetType.
        /// </summary>
        /// <typeparam name="TMessage">The type of message that will be sent.</typeparam>
        /// <typeparam name="TTarget">The type of recipients that will receive the message. The message won't be sent to recipients of another type.</typeparam>
        /// <param name="message">The message to send to registered recipients.</param>
        /// <NOTE>
        /// SuppressMessage is used by System.Diagnostics.CodeAnalysis. When you are applying code analysis to your project you will sometimes
        /// get warnings that you want to ignore. You do that by using SuprpressMessageAttribute. Now code analysis is built into the "higher" SKU's
        /// of Visual Studio but previously you had to use the tool named FxCop to prerform the analysis. Using code analysis on your code will not only
        /// increase the quality of your code but you might also learn a few things in the process.
        /// http://stackoverflow.com/questions/11910764/whats-the-use-of-supressmessage-attribute
        /// </NOTE>
        [SuppressMessage(
            "Microsoft.Design",
            "CA1004:GenericMethodsShouldProvideTypeParameter",
            Justification = "This syntax is more convenient than other alternatives.")]
        public virtual void Send<TMessage, TTarget>(TMessage message) { SendToTargetOrType(message, typeof(TTarget), null); }

        /// <summary>
        /// Sends a message to registered recipients. The message will reach only recipients that registered
        /// for this message type using one of the Register methods, and that are of the targetType.
        /// </summary>
        /// <typeparam name="TMessage">The type of message that will be sent.</typeparam>
        /// <param name="message">The message to send to registered recipients.</param>
        /// <param name="token">A token for a messaging channel. If a recipient registers using a token, and a sender sends a message using the same token,
        /// then this message will be delivered to the recipient. Other recipients who did not use a token when registering (or who used a different token)
        /// will not get the message. Similarly, messages sent without any token, or with a different token, will not be delivered to that recipient.</param>
        public virtual void Send<TMessage>(TMessage message, object token) { SendToTargetOrType(message, null, token); }

        /// <summary>Unregisters a messenger recipient completely. After this method is executed, the recipient will not receive any messages any more.</summary>
        /// <param name="recipient">The recipient that must be unregistered.</param>
        public virtual void Unregister(object recipient)
        {
            UnregisterFromLists(recipient, recipientsOfSubClassesAction);
            UnregisterFromLists(recipient, recipientsStrictAction);
        }

        /// <summary>
        /// Unregisters a message recipient for a given type of messages only. After this method is executed, the recipient will not receive messages
        /// of type TMessage anymore, but will still receive other message types (if it registered for them previously).
        /// </summary>
        /// <typeparam name="TMessage">The type of the messages that the recipient wants to unregister from.</typeparam>
        /// <param name="recipient">The recipient that must be unregistered.</param>
        /// <NOTE>
        /// SuppressMessage is used by System.Diagnostics.CodeAnalysis. When you are applying code analysis to your project you will sometimes
        /// get warnings that you want to ignore. You do that by using SuprpressMessageAttribute. Now code analysis is built into the "higher" SKU's
        /// of Visual Studio but previously you had to use the tool named FxCop to prerform the analysis. Using code analysis on your code will not only
        /// increase the quality of your code but you might also learn a few things in the process.
        /// http://stackoverflow.com/questions/11910764/whats-the-use-of-supressmessage-attribute
        /// </NOTE>
        [SuppressMessage(
            "Microsoft.Design",
            "CA1004:GenericMethodsShouldProvideTypeParameter",
            Justification = "This synatx is more convenient than other alternatives.")]
        public virtual void Unregister<TMessage>(object recipient) { Unregister<TMessage>(recipient, null); }

        /// <summary>
        /// Unregisteres a message recipient for a given type of messages only and for a given token. After this method is executed, the recipient will not recieve messages
        /// of type TMessage anymore with the given token, but will still receive other message types or messages with other tokens (if it registered for them previously).
        /// </summary>
        /// <typeparam name="TMessage">The type of messages that the recipient wants to unregister from.</typeparam>
        /// <param name="recipient">The recipient that must be unregistered.</param>
        /// <param name="token">The token for which the recipient must be unregistered.</param>
        [SuppressMessage(
            "Microsoft.Design",
            "CA1004:GenericMethodsShouldProvideTypeParameter",
            Justification = "This syntax is more convenient than other alternatives.")]
        public virtual void Unregister<TMessage>(object recipient, object token) { Unregister<TMessage>(recipient, token, null); }

        /// <summary>
        /// Unregisters a message recipient for a given type of messages and for a given action. Other message types will still be transmitted
        /// to the recipient (if it registered for them previously). Other actions that have been registered for the message type TMessage and
        /// for the given recipient (if available) will also remain available.
        /// </summary>
        /// <typeparam name="TMessage">The type messages that the recipient wants to unregister from.</typeparam>
        /// <param name="recipient">The recipient that must be unregistered.</param>
        /// <param name="action">The action that must be unregistered for the recipient and for the message type TMessage.</param>
        public virtual void Unregister<TMessage>(object recipient, Action<TMessage> action)
        {
            UnregisterFromLists(recipient, action, recipientsStrictAction);
            UnregisterFromLists(recipient, action, recipientsOfSubClassesAction);
            Cleanup();
        }

        /// <summary>
        /// Unregisters a message recipient for a given type of messages, for a given action and a given token. Other message types will still be transmitted
        /// to the recipient (if it registered for them previously). Other actions that have been registered for the message type TMessage, for the given recipient
        /// and other tokens (if available) will also remain available.
        /// </summary>
        /// <typeparam name="TMessage">The type of messages that the recipient wants to unregister from.</typeparam>
        /// <param name="recipient">The recipient that must be unregistered.</param>
        /// <param name="token">The token for which the recipient must be unregistered.</param>
        /// <param name="action">The action that must be unregistered for the recipient and for the message type TMessage.</param>
        public virtual void Unregister<TMessage>(object recipient, object token, Action<TMessage> action)
        {
            UnregisterFromLists(recipient, token, action, recipientsStrictAction);
            UnregisterFromLists(recipient, token, action, recipientsOfSubClassesAction);
            Cleanup();
        }

        private struct WeakActionAndToken
        {
            public WeakAction Action;
            public object Token;
        }
    }
}
